Abstract
Thermoelectric performance of p-type skutterudites currently lags that of the corresponding n-type materials and improvement of this important class of materials have become the focus of considerable research effort world-wide. Recent calculations find promising band structural features in p-type skutterudite materials of the type AeFe3NiSb12 ( Ae = Ca, Sr, or Ba) which could potentially lead to excellent thermoelectric properties. Recent work on the Yb- filled analog of the these formulations (YbFe3NiSb12) however finds that the onset of intrinsic conduction at lower than expected temperatures deteriorates the performance above 500 K leading to poor performance in the temperature range of interest for automotive waste heat recovery applications. We therefore seek a way to increase the band gap in order to find a way to minimize the deleterious effects of intrinsic conduction. Here we present ab initio band structure calculations and the synthesis and thermoelectric properties of YbxFe4-yPtySb12 (0.8 ≤ x ≤ 1, y = 1 and 0.5). Ab initio calculations find that the band gap increases for YbFe3PtSb12 as compared to the Ni-containing analog, though no such increase in the band gap energy was found for as compared to YbFe3.5Ni0.5Sb12. The y = 1 samples shows a characteristic transition to intrinsic conduction with a decrease in the Seebeck coefficient at temperatures above 700 K. The increased carrier concentration in y = 0.5 virtually eliminates any evidence of intrinsic conduction and the Seebeck coefficients for these samples increase monotonically up to 750 K, resulting in power factors approaching 27 W/cm∙K2 at 750 K. These power factors combined with low thermal conductivity result in a ZT = 0.9 at 750 K for Yb0.95Fe3.5Pt0.5Sb12.
